Plug and Play for Sensors Makes Good Sense

By Michael E. Los

These days, when we connect a printer or a digital camera to our computer, we expect the computer to recognize the device and automatically configure itself to be compatible with it. This ability is called "plug and play."

Plug and play will allow sensor systems to adapt to many different tasks.

But it's not just devices that need to be recognized and accepted. Information in all its varied formats demands plug and play capabilities as it travels between systems. The World Wide Web is a prime example of information plug and play. The average user just starts up his favorite Web browser and can access all kinds of information content; he does not need to know about data format standards.

Plug and play at the information level is essential for the development of netted sensor systems and facilitates easy access to information gained from the sensor network so that its full value can be realized. The information in a netted sensor system includes not only sensor measurements, but sensor capability descriptions, control messages, data requests and queries, and device status and health. To conserve limited memory and communication resources, the standard practice is to define custom data structures for use in a specific netted sensor system. The cost of this optimization is that a sensor node developed to perform one function—such as the acoustic detection of vehicles—often cannot be re-used in a netted sensor system devoted to another function without writing new code to account for different data representations.

Information plug and play would allow a netted sensor system to pursue different missions without needing to be redesigned. Plug and play would make it possible to rapidly insert or replace algorithms in a netted sensor system without affecting the system's other network elements.

As part of the Netted Sensors Initiative, MITRE is using open standards and layered architectures to develop a prototype framework for hosting information services that may exist in a netted sensor system. These information services will provide both general capability, such as data access and persistence, and specialized information processing capability, such as detection, classification, and tracking. New applications could tie into existing sensor data feeds without affecting the sensors. New sensors could be incorporated into the network without degrading the performance of existing applications.

Open Standards

In order for netted sensors to be able to plug and play, standard approaches to information representation need to be adopted. Such standards would allow sensors, instruments, imaging devices, and sensor data repositories to be accessed and, in some instances, controlled via the Web. Through our collaboration with the Open Geospatial Consortium (OGC), MITRE is influencing the development of these standards to ensure that they serve the needs of the Department of Defense and other government agencies.

OGC is developing the standards SensorML and TransducerML. SensorML provides a standard schema for metadata that describes sensor and sensor system capabilities. TransducerML describes how to capture and time-stamp sensor data for streaming between a sensor and a processor. OGC is also developing standards to define Web services that provide access to sensor capabilities. These include Sensor Planning Service, Sensor Observation Service, and Sensor Alert Service. These Web service specifications define how data collection requests are expressed, observations retrieved, and alert or alarm conditions defined.

Layered Architectures

The challenges a netted sensor system faces in managing information are no different from those faced by any distributed system of cooperating and collaborating processes: data modeling and representation, persistence, access, discovery, delivery, dissemination, pedigree, filtering, and fusion. Capabilities that meet these challenges form a framework of information services. If cleverly constructed, an information service framework could provide a netted sensor system with plug and play capability.

In its role as technical advisor to the U.S. Air Force's Electronic Systems Center (ESC), MITRE is helping the Air Force lead the way toward information level plug and play by building on the vision laid out in the ESC systems engineering Strategic Technical Plan (STP). This plan emphasizes the importance of layered architecture and loosely coupled services as key design principles for implementing systems that can work together as one enterprise to achieve net-centric capabilities. The STP vision supports five layers—applications, information infrastructure, networks, sensors, and information assurance. Of particular importance is the sensors layer, which makes unprocessed and semi-processed data available through well-known interfaces to other system components. This concept is often referred to as "post before process" and is essential for bringing information plug and play capabilities to netted sensors.

In designing a prototype framework for hosting information services that may exist in a netted sensor system, MITRE has devised and successfully demonstrated a simple message-based tasking strategy for controlling a network camera. MITRE has also succeeded in demonstrating how a collection of standards-based SensorML documents can be used to generate a visual representation of the sensing capabilities and state of a sensor network. Through our collaboration with OGC and the Air Force, we are helping develop a vision and implementation strategy for sensor information plug and play in netted sensor systems. MITRE's research also has supplied practical experience in the application of open data and protocol standards to experimental netted sensor systems. Such practical experience will allow MITRE to counsel its sponsors on the advantages and costs associated with particular netted sensor systems.

For more information, please contact Michael E. Los using the employee directory.

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